People enjoy the May Day sun in Brighton as Britain's warm spell continued. Photograph: Connors Brighton/John Connor Press

Another double bank holiday weekend was marked by the continuing spell of blazing weather that is expected to set new records for April, although rescue workers found themselves dealing with problems created by the high temperatures.

Three people who took to sea in an inflatable dinghy equipped only with one paddle and a bottle of wine were eventually rescued on Sunday after 11 hours drifting in the English Channel. They believed they had reached France, and courteously greeted their rescuers with "Bonjour!"

Their voyage began on Saturday night, when they put out from Littlehampton beach in West Sussex. They were spotted at 8am yesterday by a birdwatcher who saw them waving for help.

They were rescued by the RNLI, treated for hypothermia, checked over at Worthing hospital, and pronounced no worse for their ordeal. Nick White, of the RNLI lifeboat unit, said: "These three gents were extremely fortunate to be seen by a vigilant member of the public, and so lucky to have survived overnight with no protection and no lifejackets."

In Oxford, May Day dawned bright and clear, greeted as it has been for at least 300 years by choristers singing a hymn from the top of Magdalen College's tower.

For the past five years the nearby bridge has been closed, after a spate of injuries caused by dawn revellers jumping from it into the river. This year the bridge opened again, but the water levels were so low after months of exceptionally low rainfall that only a few waded in from the bank into water barely deep enough to swim.

The Met Office is still compiling the final sunshine and temperature returns for April, but expects it to be one of the hottest on record – slightly cooler on average than the scorching Easter weekend, when most of Britain was hotter than the south of France or Spain, but still around 20C or above in many places and set to continue.

Firefighters in Lancashire were out in force over the weekend to control a major moorland blaze in parched grass and bracken between Bolton and Chorley. Fire services appealed to walkers to take particular care.

The police and fire service in Northern Ireland warned hill walkers and holiday-makers to avoid the Mourne Mountains over the coming days as they tackle a string of blazes. Firefighters reported seeing 40ft high flames at the height of the emergency, and they fear that as they bring the fires under control it is possible they could spread again.

While there are no reports of injuries, the emergency services warned the public to avoid walking or camping in the famous mountain range that runs along the Co Down coast.

The M1, only opened after a scrapyard fire in time for last weekend's bank holiday rush, was closed again near Northampton for hours, when a woman threatened to jump from a bridge. Police negotiators talked her down safely.

A surfer died after getting into difficulty in the sea off Lowestoft in Suffolk. The emergency services were called to the beach at midday on Saturday, when watchers saw he was in trouble. A Suffolk police spokeswoman said that he was rescued from the water and treated at the scene, but pronounced dead. He has not been named, but was in his 30s and from London.